🚀 go-pugleaf

Alistair <NoSpamPlease@Somewhere.Com> writes:

> Me : "I can't pass the pointer of a class function to CreateThread"
>
> Gambit : "Well, technically you can, but not easily.
> 	You would essentially have to use a proxy function
> 	in order to do it.  Using a static method is easier,
> 	though, especially since CreateThread() allows a
> 	user-defined value to be passed to the thread instance.
> 	That makes a proxy function unnecessary."
>
> You got me thinking Gambit, how would you create a proxy function to
> make a call back of type 'void Do()' take a 'void myclass::Do()'?

That's what I'd try:

CreateThread() is declared like this:

HANDLE CreateThread(
  LPSECURITY_ATTRIBUTES lpThreadAttributes,
  SIZE_T dwStackSize,
  LPTHREAD_START_ROUTINE lpStartAddress,
  LPVOID lpParameter,
  DWORD dwCreationFlags,
  LPDWORD lpThreadId
);

lpStartAddress can be used to pass the address of the callback
function, and lpParameter for the address of the callback object.

So something like this should work:

class ThreadFunction
{
  public:
    virtual DWORD execute() = 0;

    HANDLE startThread();
};

DWORD WINAPI callbackFct(LPVOID lpParameter)
{
  assert(lpParameter!=0);
  ThreadFunction *tf(static_cast<ThreadFunction *>(lpParameter));
  return tf->execute();
}

HANDLE ThreadFunction::startThread()
{
  return CreateThread(a1,a2,&callbackFct,this,a3,a4);
  // for some appropriate a1..a4
}

Since the function called back is to return a DWORD, I think that
should also be the return type of execute().

callbackFct is the proxy function. Technically, it can't be a static
member of a class (although you may get away with one using most
implementations), but it can well be a non-member function defined in
the unnamed namespace of the translation unit defining
ThreadFunction::startThread().